This invention relates to a gas bag module for a vehicle occupant restraint system.
A typical gas bag module comprises an inflatable gas bag, a compressed gas source and a fabric layer arranged into he interior of the gas bag for guiding a stream of compressed gas emerging from the compressed gas source upon inflation of the gas bag. When using such modules in vehicle occupant restraint systems, in particular driver and passenger gas bags, the problem frequently occurs that during the inflation the speed of the gas bag in the direction of the vehicle occupant is to high that the same is injured due to this collision with the gas bag. This is the case above all when the vehicle occupant is bent forward or to the side.
It is known to use means for deflecting the compressed gas used for inflating the gas bag, which compressed gas normally flows out of a compressed gas source in the direction of the vehicle occupant, such that the compressed gas flowing into the gas bag chiefly flows in a plane vertical to the direction in which the gas bag emerges from a housing accommodating the same in the folded condition. Due to this measure, the gas bag first of all spreads in lateral direction, and the component of the speed in forward direction is reduced. It is important that the stream of gas out of the compressed gas source is not impeded, as the period within which the gas bag must be inflated is very short and must be observed by all means.
For deflecting the stream of compressed gas, there are used for instance layers of fabric which are fixed to the gas bag wall above the inlet opening of the gas bag, through which opening the compressed gas flows into the gas bag, and which have openings through which the gas flows into the actual gas bag. In this arrangement it is disadvantageous that upon impingement of a stream of compressed gas having a high pressure, a fabric layer is deformed such that the gas guiding means through the fabric layer is deteriorated. In addition, a certain distance of the fabric layer from the compressed gas source must be maintained if a pyrotechnical gas generator is used, as otherwise the fabric layer can be damaged by the hot gases.
It is also known to deflect the compressed gas by so-called diffusers directly upon emerging from the compressed gas source. For this purpose, the gas outlet openings of the compressed gas source are designed such that the stream of gas leaves the same in a certain preferred direction. It is also known to provide the compressed gas source with a cover with correspondingly shaped gas outlet openings. Since the compressed gas sources only have a small width as compared to the gas bag, only a short guidance of the stream of gas can be realized in this way.
It is the object of the invention to improve the gas guiding means in a gas bag in a plane vertical to the direction in which the gas bag emerges from a housing, or in a plane parallel to the inlet opening, and to reduce the speed of propagation of the gas bag in the direction of the occupant. This is achieved in a gas bag module which comprises an inflatable gas bag having an interior, a compressed gas source and a fabric layer arranged in the interior of the gas bag. The fabric layer guides a stream of compressed gas emerging from the compressed gas source upon inflation of the gas bag. A guiding plate is provided in the interior of the gas bag as an additional gas guiding means. Accordingly, two gas guiding means are disposed in the gas bag, namely on the one hand the layer of fabric and on the other hand the guiding plate. Due to the cooperation of the two gas guiding means, the stream of compressed gas can be directed in the desired direction. The stream of hot gas under a high pressure is deflected by the guiding plate without deforming the guiding plate and without the guiding plate being damaged by the hot gas. The fabric layer subsequently guides the stream of gas over a wide area, as the fabric layer, which is flexible and can be folded together with the gas bag, can extend over a much larger expansion than the guiding plate.
A particularly good effect is achieved when the guiding plate is disposed directly above the inlet opening of the gas bag. The compressed gas is thus guided in the desired flow direction without unnecessary deviations. Moreover, this is a very space-saving arrangement for the guiding plate.
Advantageously, the guiding plate is formed integrally with a gas bag holder, for instance as fastening frame disposed in the interior of the gas bag. In this case, the guiding plate also serves to fasten the gas bag at the gas generator or some other part of the module.
Preferably, the guiding plate has lateral openings for the passage of compressed gas. Due to the lateral arrangement of the openings, the flow direction of the gas is predetermined. The deflection angle may be chosen relatively large, e.g. in the range of 90xc2x0.
To improve the gas guiding means, the guiding plate may be provided with guiding surfaces, which direct the compressed gas flowing out of the compressed gas source in the desired direction. These guiding surfaces, which may extend over the entire width of the guiding plate, guide the stream of gas in the desired direction upon emerging from the openings and reduce the expansion of the stream of gas. By changing the angles of the guiding surfaces, the guiding plate can easily be adapted to various applications, e.g. in different types of vehicle.
Advantageously, the openings and the guiding surfaces are formed at two opposite sides of the guiding plate.
The desired flow direction is predetermined by the orientation of the guiding plate, where in this context the preferred flow direction is understood to be both the direction of outflow from the openings on the one side of the guiding plate as well as the direction opposite thereto, namely the direction of outflow from the other openings of the guiding plate. The flow direction preferably lies in a plane vertical to the direction in which the gas bag emerges from a housing or in a plane parallel to the inlet opening of the gas bag.
In a preferred embodiment of the invention, the fabric layer is disposed above the guiding plate. In this way, the hot compressed gas under a high pressure first of all meets the guiding plate preferably made of metal, which directs the stream of gas through laterally disposed outlet openings as well as adjoining guiding surfaces in the desired direction without a major reduction of kinetic energy. After the gas has left the guiding surfaces, the stream of gas expands, with the flow directions of the gas deviating more and more from the preferred direction. The fabric layer, which is mounted at a suitable distance from the guiding plate and extends parallel to the guiding plate, now directs this expanded stream of gas, whose kinetic energy and temperature are already distinctly smaller than at the moment of exit from the compressed gas source, further in the desired direction and guides the same over a much larger extension than that of the guiding plate in lateral direction. At the ends of the fabric layer, the stream of gas flows around the same, and the gas escapes into the gas bag, which due to the guidance of the compressed gas expands more in a lateral direction and less in the direction of the vehicle occupant.
The guidance of the gas by the fabric layer is particularly effective when the fabric layer is fixed to the gas bag walls in such a way that it extends parallel to the flow direction. It can thus be ensured that the flow cross-section for the compressed gas is large enough so as not to impede the flow of compressed gas.
In particular for passenger gas bags it is advantageous when the fabric layer is disposed asymmetrically with respect to the guiding plate. Since passenger gas bags often have an asymmetrical shape, e.g. a smaller extension upwards in the direction of the roof or the windshield than downwards in the direction of the legs of the vehicle occupant, it is recommended to adapt the fabric layer for the guidance of the gas to the shape of the gas bag.
In another advantageous embodiment of the invention the gas bag has a covering part partly parallel to the guiding plate, where the fabric layer is fixed to the covering part in order to provide for a specific control of the gas flow. Fixing is preferably effected via arc-shaped seams.
To ensure that the compressed gas can flow from the volume below the fabric layer into the interior of the actual gas bag, openings are provided which are preferably formed by portions of the fabric layer which are not fixed to the gas bag. In particular in conjunction with an asymmetrically arranged fabric layer, these openings forming a flow connection from the volume disposed below the fabric layer to the interior of the gas bag should advantageously have different sizes.